IbInvInh2, a novel invertase inhibitor in sweet potato, regulates starch content through post-translational regulation of vacuolar invertase Ibl3FRUCT2

As a key enzyme in the starch and sugar metabolic pathways in sweet potato (Ipomoea batatas (L.) Lam.), the vacuolar invertase (EC 3.2.1.26) Ibl3FRUCT2 is involved in partitioning and modulating the starch and sugar components of the storage root. However, the post-translational regulation of its invertase activity remains unclear. In this study, we identified three invertase inhibitors, IbInvInh1, IbInvInh2, and IbInvInh3, as potential interaction partners of Ibl3FRUCT2. All were found to act as vacuolar invertase inhibitors (VIFs) and belonged to the plant invertase/pectin methyl esterase inhibitor superfamily. Among the three VIFs, IbInvInh2 is a novel VIF in sweet potato and was confirmed to be an inhibitor of Ibl3FRUCT2. The N-terminal domain of Ibl3FRUCT2 and the Thr39 and Leu198 sites of IbInvInh2 were predicted to be engaged in their interactions. The transgenic expression of IbInvInh2 in Arabidopsis thaliana plants reduced the starch content of leaves, while its expression in the Ib & beta;fruct2-expressing Arabidopsis plants increased the starch content of leaves, suggesting that the posttranslational inhibition of Ibl3FRUCT2 activity by IbInvInh2 contributes to the regulation of the plant starch content. Taken together, our findings reveal a novel VIF in sweet potato and provide insights into the potential regulatory roles of the VIFs and invertase-VIF interaction in starch metabolism. These insights lay the foundation for using VIFs to improve the starch properties of crops.

Automated summary

This study identified three invertase inhibitors as potential interaction partners of Ibl3FRUCT2 and confirmed IbInvInh2 as a novel VIF in sweet potato. IbInvInh2 can regulate plant starch content by inhibiting the activity of Ibl3FRUCT2, providing a foundation for using VIFs to improve the starch properties of crops.